This invention relates to a method for predicting the organic acid level in a petroleum feedstream and the use of that method. Substantial economic benefits derive from the optimal usage and improved valuation of corrosive feedstocks. Such benefits can be achieved by means of improved (i.e. more accurate, precise and rapid) methods for analyzing the corrosive organic acid content of these feedstocks which, in many cases, can be purchased at attractive prices. Additional benefits can be achieved through the use of these improved methods in conjunction with mathematical models to control process and blending apparatus and to valuate feedstocks. Applications of the means to obtain the improved organic acid content value, in conjunction with the models and control apparatus, are to predict the corrosivity towards process equipment, the value of a crude or blend for sale or purchase, the recipe for crude or feed blending to a target corrosivity or organic acid level and optimization of processes to reduce the corrosive organic acid species. The improved method for predicting the organic acid content is more accurate, repeatable, and rapid than existing methods and, unlike such existing methods, can be implemented for batch or continuous on-line operation.
Currently, producers, materials engineers, plant process operators and planners, and raw materials purchasers estimate corrosivity caused by the organic acids in the materials from the Total Acid Number (TAN), or a parameter derived therefrom, obtained by a commonly accepted potassium hydroxide titration method, one example being ASTM D664.
The ASTM D664 method, while the most commonly used method in the petroleum industry for determining organic acids in petroleum streams, is not selective to organic acids. It reports, as acids, any species that utilizes the potassium titrant in reaction, complexation, neutralization, or replacement. For example, one limitation of the current ASTM method is its inaccuracy in determining the correct acid content when the material has di- and trivalent metal acid salts, such as calcium naphthenates. Use of the ASTM TAN method on materials that contain calcium naphthenates would over-report the TAN since both true acid content as well as the calcium salts would be reported as TAN. Hence the corrosivity of the materials, as determined from mathematical models relating corrosion rates to the TAN value for these materials, would be over-estimated in such cases.
This invention includes, in all of its embodiments, a method to predict the organic acid content from the infra-red (IR) spectrum of a petroleum feedstock or process fluid. The IR method reports the organic acid content in units of titratable organic acid, TAN. The TAN determined by IR, henceforth called IR TAN, therefore, can be used in applications and models that use TAN as an input parameter. The IR TAN method is shown to be statistically equivalent to ASTM TAN and be more accurate than ASTM when calcium acid salts are present in the materials.
High TAN crudes can be purchased, in many cases, at attractive prices. The improved method for TAN measurement, as incorporated in the present invention, is a key enabler for reducing feed costs through the increased usage of such economically attractive materials.